Sound-recording system



Dec. 16, 1930. E, cf WEN-TE 1,784,858

SOUND RECORDING SYSTEM Filed 'Feb. 10', 1928 5 AMPz/F/ER AMPLIFIER flier/HER /Nl E/V7'0R fDWARD LI WENT/E- 5y Aim/Wm all s'rrss PQATENT WW G. WENTE, OF NEW YO 1?. iii, AQSIGNOB TO BELL TELEPHONE LABO- l i" if INCOOIEATED, h" NEW YORK, N. Y., A CORPORATION OF N YOlltlti.

BOUND-RECORDING SYSTEM application filed February 10, 1928. Serial No. 253,259.

This invention relates to sound recording systems and more particularly to methods 0 volume control for such systems.

' It is well known in the art that when a a record of sound in made on a wax disc or a V photographic film, the range of intensity that can he recorded and successfull reproduced is limited on one side by amp itude distortion and on the other by the inherent irreguio larities in the recording medium which gives rise to the scratch during reproduction. lln order to increase this range of volume, various methods have been suggested for reducing the amplification .durlng recording when the intensity is high, and increasing it when the intensity is low. lhe amplificatlon in reproducing is then correspondingly decreased and increased in order to reproduce the sound at the original intensities.

The satisfactory operation of such arbitrary methods, however, requires that an operator shall anticipate changes of intensities and thereby prevent the record capacity from hein exceeded. It is the general ob]ect of this lnvention to accomplish this result automatically.

Accordingly it is proposed that the recording he done in a large pro erly damped room. The sound sourcean the pick-up ao microphone are placed at o posite ends of the room and the time dela 1n the arrival of the sound waves at the microphone thereby introduced, permits the ain in the recording circuit to be varied by firtpick-up of a second microphone located near the sound source, hefore the corresponding changes in the sound currents occur.

la the drawing 1 is a recordin studiol W oi the sound source by about 1/25 of a second.

While the sound is bein recorded the pick up of the control microphone 8 is energlzing fast operating marginal relays 9, 10 and 4: through amplifier 11 and rectifier 12.' The amplification of amplifier 11 is adjusted so that relay 4 operates when the sound intensit is about to exceed the capacity of the recor ing film. Accordingly, almost simultaneously with the increase of sound intensity above a predetermined level, relay l'will attract its armatures to open the recording circuit at contact 13 and reclose it at contact 14. The light valve is then no-longer connected across the entire potentiometer for its circuit isnow traced from terminal 15 and conductor 17 and terminal 16, conductor 18, contacts 19 and 14 and conductor 20 to the light valve 6.

Due to the delayed arrival of the sound cur- "if the sound becomes extremely loud. lln this extreme case the recording clrcuit is traced from terminals 15 and conductor 17 and terminal21, conductor 22, contacts 23, 24:, 14 and conductor 20 to the light valve 6.

Conversely, as the sound intensity decreases relays 9, 10 and 4 will be successively released and the recording light valve connected to terminal 25, 16 or 26 respcctivel to prevent the sound currents from falling helow a predetermined minimum value.

- lln order that the record so made may he reproduced at the proper relative intensity throughout, some such marking devices as lamps 27 28 and 29 may be provided in the recorder. In the arrangement shown the "lps are related to marginal relays d, 10

operated. Lig t from these lps y u the film through small apertures 31, 32 and 33 which are slightly displaced laterally from each other, and leaves a line or lines upon the film to one side of the sound record in accordance with the amount of volume compression introduced.

\ The reproducer would then be provided with a relay operated potentiometer for introducing in the reproducer circuit proper amounts of gain to compensate for the losses occurring in the recording potentiometer.

The relays of this potentiometer could be con- I trolled by contact devices operating through (ill perforations in the film where the markings occur or by light sensitive cells responsive to the variations of light beams caused by the film markings when the beams are projected through the film.

The present invention has been illustrated by a specific method of volume control but obviously many modifications might be made without departing from the spirit and scope of the invention defined in the following claims.

What is claimed is 1. In a sound recording system; a recording surface, a source of sounds to-be recorded,

a pick-up device at a distance from the source for translating the sounds into corresponding electric currents, a recording circuit, and monitoring means responsive to the sounds for varying the gain in the recording circuit automatically in anticipation of changes in the amplitude of the currentsfrom the pick-' up device and for marking the recordin surface at intervals only in accordance wit the gain variations.

2. In a sound recording system, a recording surface, a source of sound, a pick-up device at a distance from the sound source for translatin the sounds into electric currents, a second pick-up device near the sound source, recording means including a recording circuit, and means responsive to the second pickup device for varying the gain in the recording circuit and marking the recording surface at intervals only in accordance with the gain variations. J

In witness whereof, I hereunto subscribe my name this 3rd day of February, 1928.

EDWARD C. WENTE. 

